Pure plant oil (PPO) or tree based oil (TBO) or straight vegetable oil (SVO) are the terms used in the context of neat biodiesel. SVO or TBO or PPO are natural oils which rarely is used as such in commercial diesel engines and their use as blends is also limited.
Natural oils also include any oil obtained from animal source as well (animal fat oil). Plant oils such as SVO or PPO or TBO and animal oils are rich in triglycerides and can be obtained by mechanical, chemical & physical processing from the respective sources.
Natural oils as blends of diesel have some properties that prevent their use in commercial diesel engines. The major ones are listed below.                1. High boiling point: Natural oils boil at higher temperature than diesel and have problems meeting the norms required for minimum distillation characteristics. This causes the residue formation in engine and in long run there will be accumulation of greasy material in the engine. This could lead to clogging, increased smoke at higher loads, increase in emission of nitrogen oxides (NOx), loss of power and mileage, sudden stoppage of engine.        2. High viscosity: Natural oils are about eight times viscous than diesel and as such cannot be used in current diesel engines without modification. Natural oil blends of diesel (below 20%) often meet the physico chemical properties of diesel and were used without any short-term issues. But in long term, they cause non-uniform spraying at ignition chamber, engine deposits, inefficient burning of fuel and increase in NOx.        3. Immiscibility: Natural oils are miscible with diesel and stay miscible for 15-30 days depending on the composition of oil, but longer periods of storage cause separation of natural oils and diesel layers and in about two months storage, almost complete separation occurs. The separated layer looks like a brown or yellow precipitate and this causes engine deposits, sudden stoppage/malfunction of engine, increase in emission of particulate matter, etc.                    The main issues with respect to diesel engine by use of blends of natural oils with diesel are                        
IssuesReasonPossible solutiona)CloggingDeposits and greasyGrease or enginematerial forming indeposit formationengineneed to beprevented(transesterificationof natural oil is onemethod)b)Increase inImproper mixing ofMiscibility withsmokenatural oils and diesel,diesel need to begradual separation ofimproved (bylayersadding someadditives)c)IncreaseAny strain on fuelFuel injected needin NOxdelivery/burningto be uniform incauses increase incomposition andNOx. Strain in fuelqualitydelivery is mainlycaused by non-uniformity of fuel.d)Loss of powerEven though naturalSeparation ofand mileageoils have rich oxygennatural oils andcontent and higherdiesel layers is thecalorific value thanmain cause anddiesel, loss of powernatural oils needsand mileage occur dueto be madeto non-uniformity ofcompletelyfuel.miscible withdiesele)Sudden stoppageIncrease in moistureThe waxy or greaseof enginecontent in engine duesolid formationto the waxy solidneed to be avoideddeposition attractsand any free fattydust and moreacids or partiallymoisture that arehydrolysedretained inside thetriglyceridesengine. Eventually,present in naturalthese enter theoils need to beignition chambersolubilized incausing abrupt changediesel.in fuel behaviorcausing suddenstoppage of engine.f)Engine depositsSeparation of naturalNatural oils (SVO)oils and diesel andare highly viscoustheir in turn assistanceliquids with minutein accumulation ofpercentage of freedust and moisture isfatty acids orresponsible for enginepartiallydeposits.hydrolysedtriglycerides(diglycerides,monoglycerides)produced duringmechanical orsolvent basedprocessing ofseeds/bark/leaves.These free fattyacids precipitatefrom blendeddiesel within oneday and increasethe engine depositformation andsomehow thesefatty acids need tobe solubilized indiesel.g)Increase inEngine deposits andElimination of anysound fromnon uniformity of fuelinsoluble particleengineflow results in stressin blended dieselon compressionand ensuringignition system,uniform flow ofwhich results infuel.increased noise
It is clearly understood from above table that most of the problems caused by natural oil blends with diesel is immiscibility. When the natural oil has the property of not being soluble in diesel, the above problems like engine deposits, increase in NOx emission, increased smoke, decrease in power and mileage, etc occur.
To address the problems associated with use of natural oil in diesel, biodiesel manufacturers use transesterified oil obtained through transesterification reaction. This way the triglycerides are converted to free fatty acids and the fatty acids are in turn esterified with methanol or ethanol (use of higher alcohols is also reported). The hydrolysis process involves use of sodium hydroxide and methanol and is a heat intensive process (lot of heat from environment to be supplied). There is increasing criticism that whatever benefit derived by shifting to renewable plant based oils (reduction in carbon dioxide, lower pollution, etc), is being lost by use of toxic industrial chemicals (like methanol), problems with waste disposal, increased heat input etc.
Hence, there is a need for development of methods to avoid transesterification of natural oils. A process to convert the natural oils to a diesel blend product is credible, but identifying compounds or components which can stabilize natural oil blends will be of great interest and could provide a cheaper, safer and environmentally friendly alternative to transesterification, help in reduction of pollution, carbon dioxide emissions, decrease in byproduct toxicity, no heat input from environment, etc.
PCT/US99/00598 discloses an additive composition consisting of water soluble alcohols. All the composition disclosed in PCT/US99/00598 shows the presence of water and ethanol.
Yoshimoto et al (Published by society of automotive engineers, 400 commonwealth drive, Warrendale, Pa.-15096, USA, October 2002) discloses performance of a diesel engine by the blends of rapeseed oil and oxygenated organic compounds such as ethanol, 1-propanol, 1-butanol, 1-pentanol, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol and dibutyl ether.
Khaled et al (1st International energy conversion engineering conference, Virginia, USA, August 2003) discloses fuel blends in compression ignition engines which fuel blend comprises iso-butanol, diesel and olive oil.
The present invention addresses the problems associated with prior art mentioned above.